The extraction of blood for hemodialysis is generally performed on a vein. However, the flow of blood in the veins, coming from the capillaries, is generally too slow for the flow required for efficient hemodialysis. In order to ensure a sufficiently fast flow of blood in the vein, a procedure is used to join an adjacent artery to the vein, allowing arterial blood to flow directly into the vein, thereby boosting its flow rate. A commonly used site is a blood vessel of the arm, e.g. at the wrist or at the upper forearm. Due to the arterial pressure, the vein should increase in size and its walls thicken, such that it is then easier to put needles into this vein to extract and to return the blood. The arterial-venous (AV) join is generally performed either directly, to produce an AV fistula, or by means of a surgically inserted artificial AV graft or shunt joining artery and vein. Shunts are inserted when the patient's native vasculature does not permit a fistula. The shunt, which may be either straight or looped, is close to the surface of the skin for easier needle insertion. The shunt may be constructed of an artificial material such as polytetrafluoroethylene or Gortex®, or can be obtained from the patient's own body such as a vein in the thigh, or from a specially treated animal blood vessel. The use of an AV shunt enables the needle access to be made in the shunt, rather than in the patient's own vein, though either procedure may be used.
However, such shunts, both of the fistula and AV type, have a problem in that they are often associated with stenosis of the vein into which they are inserted, usually just downstream from the point where the shunt has been sewn into the vein, or the point where the artery and vein are sewn together. Such venous narrowing often leads to clotting or thrombosis, and if untreated, could lead to complete blockage of the vein, often within less than a year of the insertion of the shunt. The cause for this phenomenon is unknown, but it is thought that it may be associated with the turbulent flow of the blood in that region of the vein. This stenosis has traditionally been treated by means of balloon angioplasty performed in the region downstream of the shunt.
However, this procedure is costly, involving complex instrumentation and x-ray surveillance generally available only in the hospital environment, generally has to be repeated at intervals of several months, and has the associated dangers of venous rupture if excess pressure is applied.
There therefore exists a need for an apparatus and method for preventing venous stenosis associated with the use of AV shunts, which overcomes at least some of the disadvantages of prior art systems and methods.
The disclosures of each of the publications mentioned in this section and in other sections of the specification, are hereby incorporated by reference, each in its entirety.